package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.Serializable;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.util.ArrayUtil;

/**
 *  A Payload is metadata that can be stored together with each occurrence 
 *  of a term. This metadata is stored inline in the posting list of the
 *  specific term.  
 *  <p>
 *  To store payloads in the index a {@link TokenStream} has to be used that
 *  produces payload data.
 *  <p>
 *  Use {@link TermPositions#getPayloadLength()} and {@link TermPositions#getPayload(byte[], int)}
 *  to retrieve the payloads from the index.<br>
 *
 */
public class Payload implements Serializable, Cloneable {
    /** the byte array containing the payload data */
    protected byte[] data;

    /** the offset within the byte array */
    protected int offset;

    /** the length of the payload data */
    protected int length;

    /** Creates an empty payload and does not allocate a byte array. */
    public Payload() {
        // nothing to do
    }

    /**
     * Creates a new payload with the the given array as data.
     * A reference to the passed-in array is held, i. e. no 
     * copy is made.
     * 
     * @param data the data of this payload
     */
    public Payload(byte[] data) {
        this(data, 0, data.length);
    }

    /**
     * Creates a new payload with the the given array as data. 
     * A reference to the passed-in array is held, i. e. no 
     * copy is made.
     * 
     * @param data the data of this payload
     * @param offset the offset in the data byte array
     * @param length the length of the data
     */
    public Payload(byte[] data, int offset, int length) {
        if (offset < 0 || offset + length > data.length) {
            throw new IllegalArgumentException();
        }
        this.data = data;
        this.offset = offset;
        this.length = length;
    }

    /**
     * Sets this payloads data. 
     * A reference to the passed-in array is held, i. e. no 
     * copy is made.
     */
    public void setData(byte[] data) {
        setData(data, 0, data.length);
    }

    /**
     * Sets this payloads data. 
     * A reference to the passed-in array is held, i. e. no 
     * copy is made.
     */
    public void setData(byte[] data, int offset, int length) {
        this.data = data;
        this.offset = offset;
        this.length = length;
    }

    /**
     * Returns a reference to the underlying byte array
     * that holds this payloads data.
     */
    public byte[] getData() {
        return this.data;
    }

    /**
     * Returns the offset in the underlying byte array 
     */
    public int getOffset() {
        return this.offset;
    }

    /**
     * Returns the length of the payload data. 
     */
    public int length() {
        return this.length;
    }

    /**
     * Returns the byte at the given index.
     */
    public byte byteAt(int index) {
        if (0 <= index && index < this.length) {
            return this.data[this.offset + index];
        }
        throw new ArrayIndexOutOfBoundsException(index);
    }

    /**
     * Allocates a new byte array, copies the payload data into it and returns it. 
     */
    public byte[] toByteArray() {
        byte[] retArray = new byte[this.length];
        System.arraycopy(this.data, this.offset, retArray, 0, this.length);
        return retArray;
    }

    /**
     * Copies the payload data to a byte array.
     * 
     * @param target the target byte array
     * @param targetOffset the offset in the target byte array
     */
    public void copyTo(byte[] target, int targetOffset) {
        if (this.length > target.length + targetOffset) {
            throw new ArrayIndexOutOfBoundsException();
        }
        System.arraycopy(this.data, this.offset, target, targetOffset, this.length);
    }

    /**
     * Clones this payload by creating a copy of the underlying
     * byte array.
     */
    @Override
    public Object clone() {
        try {
            // Start with a shallow copy of data
            Payload clone = (Payload) super.clone();
            // Only copy the part of data that belongs to this Payload
            if (offset == 0 && length == data.length) {
                // It is the whole thing, so just clone it.
                clone.data = data.clone();
            } else {
                // Just get the part
                clone.data = this.toByteArray();
                clone.offset = 0;
            }
            return clone;
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException(e); // shouldn't happen
        }
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == this)
            return true;
        if (obj instanceof Payload) {
            Payload other = (Payload) obj;
            if (length == other.length) {
                for (int i = 0; i < length; i++)
                    if (data[offset + i] != other.data[other.offset + i])
                        return false;
                return true;
            } else
                return false;
        } else
            return false;
    }

    @Override
    public int hashCode() {
        return ArrayUtil.hashCode(data, offset, offset + length);
    }
}
